Time base circuit for cathode-ray tubes



July 26, 1949.

R. HILTON TIME BASE CIRCUIT FOR CATHODE-RAY TUBES Filed Feb. 19, 1945 2 Sheets-Sheet l FUCHS' Inventor [ym H] LTO N July 26, 1949.A R, Hlm-QN `2,476,978

TIME BASE CIRCUIT FOR GATHOD-RAY TUBES Filed Feb. 19, 1945 2 SheetS-Shee-t 2 s l s l t I Il; 647.40051 V2 /l/vaof' l (r/ME B455 l wwf/roma) n BACK I I I 1 V3 DE-ION/SES Invenlor Patented July 26, 1949 FICE TIME BASE CIRCUIT FOR CATHODE-RAY TUBES Roy Hilton, London, England, assignor, by mesne assignments, to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application February 19, 1945, Serial No. 578,744 In Great Britain February 3, 1944 8 Claims.

This invention relates to time-base circuits for the production of saw-toothed impulses, that is impulses consisting of a slow stroke or sweep and a quick stroke or return; and more particularly to trigger-operated time-base circuits, that is to say time-base circuits in which a single sawtoothed pulse is produced in response to a stimulus. Such circuits are already known and have been used in connection with oscillographs for producing a time-base deection and in television equipment for controlling a scanning device. In such uses the impulse in the form of a voltage is applied across the X-plates of a cathode-ray tube so that the luminous spot on the screen is made to travel in one sense at a slow uniform rate and in the opposite sense at aratel that is made as quick as possible.

An object of the invention is to reduce as much as possible the time delay between the reception of a stimulus and the commencement of the slow stroke or sweep.

Another object of the invention is to provide a time-base circuit that is so fast in its response to a stimulus that when used in conjunction with an oscilloscope the stimulus can be provided by the wave-front of the signal that is to be observed during the sweep of the impulse so stimulated.

In actual embodiments of the invention the delay between triggering and the commencement of the sweep has been reduced to something of the order of one microsecond, and has had a maximum value of about ten microseconds. The necessity of providing a stimulating signal in advance of the signal to be observed is thus avoided.

Also, if the triggering pulse is reouired as a reference point, this point is located within about l roicrosecond at the beginning of the sweep.

It is to be further noted that a circuit in accordance with the present invention can provide a sweep duration which is quite independent of the duration of the triggering pulse. The commencement of the sweep is determined by the front of the triggering signal, whilst the end of the sweep is determined purely by the constants in the condenser charging circuit and the presetting of a discharge device across the con` The description that now follows relates to the accompanying drawing in which:

Fig. 1 shows the basic circuit diagram of a trigger-operated time-base circuit in accordance with the present invention; and

Fig. 2 shows a number of explanatory oscillograms.

Consider first the circuit shown as the lefthand side of Fig. 1 and consisting of pentode V2 and condenser C1, connected in parallel with potentiometer R2, R1 between -l-HT and earth. The pentode V2 is a device permitting iiow'of electricity through itself at a constant rate which is dependent primarily upon its control-grid and screen-grid voltages and is substantiallyindependent of its anode voltage. Being in series with the condenser C1, the pentode V2 permits the `condenser to be charged up at a steady rate, its lower pole becoming increasingly negative with respect to its upper pole. The rate of such change is determined by the setting of the cathode voltage upon the potentiometer Rz, R1, making the control grid of the pentode more or less negative with respect to the cathode. The time-base sweep control voltage is taken 01T from the anode of V2, so that this voltage starts, if the condenser is completely discharged, from the value -l-HT, and steadily falls away. Thus it provides a change in voltage, linear with time, which when applied to the horizontal deecting plates of a cathode ray tube. causes the electron beam to move across the screenA equal distances in enual times.

This then is the part of the circuit bv which a charge is steadily built up on the condenser C1: next is to be described the means bv which the condenser is discharged suddenly. This is provided for by the circuit consisting of triggertuhe V1 and resistance Re shunted in series with one another across the condenser C1. The valve V1 is a gas-nlled triode. such that the gas therein ionises when the anode reaches a certain critical voltage positive with respect to the cathode; this critical voltage is predetermined by the setting of the grid voltage relative to the cathode as provided for by the potentiometer R4, R5. When the condenser C1 has charged up to this critical voltage, the tube V1 fires and provides a very easy discharge path for the condenser.

As now described, then, the circuit if appropriately energised will function somewhat in the manner of an oscillation generator to produce a continuous succession of saw-tooth pulses. It is desired however to trigger-operate the circuit so that the circuit will go through one complete cycle in response to a stimulus, and moreover to have a very fast response, so fast that the stimulus may be provided by the very signal that is to be observed. "'Ilh-is.trigger-mechanismwill therefore novnbeldesc'ribed: it consists=o`f a sec'ondigaslled triode V3, with associated resistances R7, Ra, R9, and condenser C2. The resistance #Rm valve V3, and resistance R8 and R1; are arranged Yin series across the high-#tension suppl-y: gv"the valve V3 has its anode connected to the anodefof'j V1 over` condenser C2 and hasitscathode .directly connected to the screen of-ith'e pentodef-Vz: AThe grid of V3 hasv a certain biason':it-,f.while alsoibeing connected to receive the triggering signal. The bias is so great that even .with .the `tull l-LJIrpotential between anode and cathode..no..dischare occurs. Consequently, when the "time base is switched on, valve V3 does not conductgantllithe screen of the pentodeVz is kept at earth poteniitial; .tiisalffeaturezot the zpentode'valve that the anode current fdependsfupon .the screengg-rid voltfiage, a'ndlini theaconditions described, :with the tscreen .'-cat :earth xpotential, no :current flows through the peht'ode .V2 and the condenser' .C1 A"doe's"mot'asharge. This means thatfthe anode of V2 will remain at a certain high positive potential `Athic'lrrliiepends,'zactuaslly, upon theratiorbetween f the-capacitan'ces :onwafter `a shortV period, Vupon 1fthe ratioiofi the insulation:resistances'of the `two JcUndensersCi-and 'C3 .which are in series :across tine' fH. Tfsupply.

litfnow' there comes overf the Vtriggering r signal Taleadeiazipcsitive'. pulserof Vsufficient amplitude; .this afp'ulse `onappli-cation: to the: grid' of "V3-will -cause fonisation .stof-occun "so that: :the valve Abecomes econducting=as=betweenitsanodeand cathodeiand @will remarinzconductingfafter :the triggering signal rfhasrceased. The.-flow Ao'f-cnnrent'in the-circuit :.R'r; VsfRs, Rsraise'sfthe potential of :the screen v.ot'valt'e V2 abruptly rto la p'osi-ti-ve cvalue'suoh that urrent 'begins tto' now through the fpentode' V2, w'chargingthe fcondenser C1. vEventually the concdenserf `C1* 1 reaches. the' lcritical '--voltage and :lires 7 tubci-Vn to1cause@anginstantaneous- :discharge` of i 'theccondenser :01. When ithis happenswthere sista Vth-isf furop 1 Afis- @appli-ed -over -condenser'- SC2 to t fthe nanode-'fof` V3, :quenching :the latter. The positive .fpbtential `:on::theesereen 'ofi-Vids thusV removed,

fand..1the-time-base circuitfis A.locked :inoperative .-1withf1thecondenservc1 discharged -tothe eX-tinguishing Voltage of V1.

ffAJneorrz 'stabiliser N1 isA shown connected' across .theescenegrd :input circuit for the .fpentod'e V2. Jlihisilimits the Yvaluecf the= positive voltage-:ap- .Jplied toY -the screen,l andrfin` particular-serves to minimise thef-eiect upon-the. screen v'oltagef=.of @the charging'current that lows:into condenser -..C2 immediately.-.upon :ringfofv-valve- Thefex- .sistenee `of y.this momentary `clfiarging current means A,that.for-itlfxat' Vshort ltime the :current u.ithroughf resistances 4.Raeand :R9 y. is I greater than normalwand the voltage..`.across fthern isy-cor-re- .spondinglywhighen -;If :this voltageis-'appledfto .,thfrxscreen .of the-.charging-pentode the ratefof charge ot, the 4sweep-condenser*will -be -increased .for an instantetthe beginningof--the'sweepgwith `a consequentspeeding'uppf athe time-base. -The -.neon cannotxdealv withthe V:initial `front on this pulse of -voltage but .it reduces v.the .duration of 'thepulse to a value .whichmakes its eiectfon the time-base.almostnegligible.

"It Vviiill thus. beV seen as one of V.the.featuresof 'lthis circuitA that. .thereis a. .very small delay .be- 4"tween triggering and commencement of the timebase sweep on the cathode ray tube, as no time is lost in discharging condenser C1 before commencing to charge it. Such delay as there is `A depends upon: the timefftaken for .the1gas-1led ftub'e V3 .tov ionise. This varies with the type of gas and the amplitude of triggering pulse. Using .a helium-filled triode, delays of a fraction of a microsecond are possible, and the delay is never 3lilelytovbemore than l0 microseconds. 3l0 In Fig. 2 is shown a set of oscillograms showing :ftheyoltageatfvarious points in the circuit during arconditiontofworking such that the triggering eperiodisgreater. than the sweep period:

Oscillogramdi shows the form of a typical trig- .15 gering signal arriving over the triggering-signal "leadandJappear'ing at that end of the resistance remote frornthe grid of tube Vs rsdillogram B shows the resultant voltage wave-form generated at the cathode of the triggwgeringwtube :V3-and A'directly vapplied .to .thef screen gridiof the -pentode V2;

.-Oscillograrn` yC `shows the `Ltirne-base voltage .-.variationlat .theanodeoff the pentode V2; the flylback .timea-fterthedischarge tube V1 has onised -isshort,but notinlnitesirnah VOscillogram .D- shows the sudden drop in the anodeevoltagewof fsaidwdischarge tube-V1 during .-.thisfybacksperiod and nally ',sOscillog-ramgE-:shows the anode voltagelof tube V3 which voltagey suddenly drops at the beginning of .thesweenA inet-when `-tuloe V3 starts to'conduct, andremainszat .this vnew-.low value .throughout the s sweepuntil fakick trom` thefanode -of V1 causes fitftodropstill urtherand ,toextinguish the tube; ?-the `voltage.:then:beginsto rise very quickly, ,but is prevented from yreaching sits full H. T, supply ``voltage instantaneously lby reason of the charge .fonthe-coupling,.condenser C2. :An exponential .r-iseeoecursvatterqaJ v'certain potential has been reached, and the circuit remains-quiescent until vtheenextl triggering-.signal 'occurs and Vthe -cycle l repeats. smallidownward-loop at. the beginning :offthersweepzappears -.to.-be*due to the neon volt- ..age dropping fbelow rits .normal 'working value Aimlf .mediatelyatter striking. Y

`.1l'ft..has )been-found thatisometimes there `has Doccurrede :small sweep, `exponential vfin vform, before-commencement of the triggered sweep. -Thisf.has been found fto be due 1to the charging .3Uof...the-. condenser C1 :through the 'coupling condenserafand the resistance R10 -which `performs ithe .functionvofial'eakf on .the-plates of the cathode ra-y '.tubefor onthe gridoi 'the `-rst valve rof an amplifier.V .fIt wouldbeespecially noticeable .if nthe .time-ibase were writing --at a :'highi'speedy and triggering-..Were at .a-.low speed, i.-e.-when there is a.comparativelylarge period 'during'which the V.timefbaseproper is inoperative During this 'ffperiodfunless'Y black-fout precautions-were taken -..there-would-fbeHafconfused oscillogramY of the lv.signakappl-ied .to the Y deiectorplates upto the -..beginning-of the --sweep proper. V`lItis therefore .desirableutot apply intensity modulation to the gridfof lathe .cathode ray tube,- and ai convenient 4signalvfor `fthis purposecan'be-obtained romthe i `.resistance.R9 in -seriesfwith Vr cathode. Normally the-.intensity .controlfcan beset soA thatnol illu- .minationof ftherscreenoccurs'but when the sweep wcommences-the sudden `rise -'in Voltagedn'the cathode of-l-Vmapplied-:to thegrid of the cathode v.ray tube giwes-the required bright-in during `.the sweeptperiod only. l'twwill` beumderstcodthatt the invention may .-.take.. othenforms.. Among the'ipos'sible modicaltions of the arrangement shown in the drawing arethe insertion of a buffer valve amplifier between V1 and V3; and again the use of a hardvalvejlimiter in the cathode circuit of V3 instead of the neon tube N1. It is convenient to have a differentiating circuit followed by an amplier with a'low output impedance, for use with this time-base as the input impedance to the grid Vcircuit of the triggering valve V3 is preferably kept low, and control over the shape and amplitude of the triggering signal helps to obtain optimum results.

What is claimed is:

1. A time base circuit responsive to trigger pulses, comprising a normally non-conductive electron discharge device of the constant-current type having a cathode, an anode and a plurality of grids, a source of space current connected across said anode and said cathode, biasing means maintaining all except one of said grids at fixed potentials relative to said cathode, a condenser inserted between said anode and the positive pole of said source, a first trigger tube connected at its cathode to said anode and shunted across said condenser, said tube being arranged to conduct upon charging oi said condenser to a predetermined voltage, a load impedance connected in series with said source and said tube, a second trigger tube having an input and an output circuit, said input circuit being adapted to receive said trigger pulses whereby said second tube will be rendered conductive and result in a change of potential at a point of said output circuit, circuit means connecting said point to said one grid of said electron discharge device so as to apply said change of potential to said one grid with a positive polarity, whereby said discharge device will become conductive and will charge said condenser until said rst trigger tube becomes energized and causes a terminal of said load impedance to undergo a change of potential, and a connection coupling said terminal to an electrode of said second tube in such manner that energization oi said first tube Will quench said second tube, whereby said one grid will be driven sufficiently negative to render said electronic discharge device non-conductive.

2. A time base circuit according to claim 1, further comprising a glow tube connected between said one grid and said cathode so as substantially to prevent the potential of said one grid from exceeding a predetermined value.

3. A time base circuit according to claim 2 wherein said electron discharge device is a pentode and said one grid is the screen of said pentode.

4. A time base circuit responsive to trigger pulses, comprising a vacuum tube of the constant-current type having a cathode, an anode, and a plurality of grids including a screen grid, a source of space current connected across said anode and said cathode, a condenser inserted between said anode and the positive pole of said source, a rst gas discharge tube connected at its cathode to said anode and arranged to be ionized by an anode-cathode voltage less than the voltage of said source, a load resistance inserted between the positive pole of said source and the anode of said first gas discharge tube, a second gas discharge tube having an input circuit adapted to receive said trigger pulses whereby said second tube will be rendered conductive, said second tube further having an output circuit including an anode resistance and a cathode resistance connected, respectively, to the positive and the negative pole of said source, a conductive connection between said screen grid anda point on said cathode resistance, biasing means maintaining all the grids of said vacuum tube except said screen grid at suchvfixved potentials relative to the cathode of said vacuum tube as to maintain said vacuum tube non-conductive in the de-ionized condition of said second gas discharge tube and conductive in the ionized condition of the latter tube, said vacuum tube when conductive beingarranged to charge'said condenser at a substantially linear rate `until said first gas discharge tube becomes ionized, whereuponv said condenser discharges through said first tube and produces a voltage drop across said load resistance, and circuit means coupling the anodes of saidV two gas discharge tubes together whereby said voltage drop will lower the anode potential of said second tube suiiiciently to quench the latter.

5. A time base circuit according to claim 4 wherein said ilrst gas discharge tube has a control grid, further comprising a source of adjustable bias for said control grid whereby the period of conductivity of said vacuum tube and of said second gas discharge tube may be varied.

6. In combination, a cathode ray tube having deflecting elements and an intensity control electrode normally biased to suppress the beam of said tube; a time base circuit connected across said deecting elements, said time base circuit comprising `a condenser, a normally non-conductive constant-current device connected in series with said condenser, means including a trigger circuit responsive to incoming pulses for rendering said device conductive whereby said condenser will be charged at a substantially linear rate, a normally blocked discharge device connected across said condenser with such a polarity as to discharge said condenser when the voltage across the latter reaches a predetermined value, means includingsaid discharge device for restoring said constant-current device to non-conductive condition upon discharge of said condenser, and a, load impedance connected in said time base circuit so that a voltage drop is produced across said impedance when said constant-current device is conductive; and circuit means coupling said load impedance to said intensity control electrode in such a manner that said voltage drop will overcome the bias of said intensity control electrode sufficiently to cause the appearance of said beam when said constant-current device is conductive.

7. In combination, a cathode ray tube having deflecting elements and an intensity control electrode normally biased to suppress the beam of said tube, a time base circuit according to claim l., iirst output means arranged to apply the alternating voltage built up across said condenser to said deecting elements, and second output means arranged to apply at least part of the potential of said one grid to said intensity control electrode in such manner that the latter electrode will be biased suiliciently positive to cause the appearance of said beam when said electron discharge device is conductive.

8. In combination, a cathode ray tube having a pair of delecting electrodes and an intensity control electrode normally biased to suppress the beam of said tube, a time base circuit according to claim 4, first output means connecting said constant-current device across said deiiecting electrodes, and second output means connecting a tap on said cathode resistance to said intensity control electrode, the potential of said tap in the ionized condition of said second gas discharge tube being: eumeiently positive. to,- cause the appenance Qt seid BOX HILTON.

REFERENCES CITED The. following refereneeare ofrecord in the file of this patent:

STATES PATENTS Number Number Name Date Schlesinger Feb. 14, 1939 Young Apr. 18, 1939 Knoop June 3, 1941 Burton June 3, 1941 Rogers Sept. 8, 1942 Smith et al. Sept. 25, 1945 Miller Dec. 24;, 1946 FOREIGN PATENTS Country Date Great Britain Oct. 9, 1941 Certificate of Correction Patent N o. 2,476,978 July 26, 1949 ROY HILTON It is hereby certified that errors appear in the above numbered patent requiring correction as follows:

In the grant, line 15, strike out the Words of seventeen years; same line, after grant insert until February 3, 1,964; in the heading to the printed specification, line 10, before 8 Claims insert Section 1, Public Law 6.90, August 8, 1946. Patent expires February 3, 1964;

and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 11th day of July, A. D. 1950.

THOMAS F. MURPHY,

Assistant ommz'ssz'aner of Patents.

Certificate of Correction Patent No. 2,476,978 July 26, 1949 ROY HILTON It is hereby certified that errors appear in the above numbered patent requiring correction as follows:

In the grant, line 15, strike out the words of seventeen years; same line, after "gran insert until February 3, 1.964; in the heading to the printed specification, line 10, before 8 Claims insert Section 1, Public Law 690, August 8, 1.946. Patent expires February 3, 1964;

and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 11th day of July, A. D. 1950.

THOMAS F. MURPHY,

Assistant Oommz'aczoner of Patents. 

